Adalimumab prevents barrier dysfunction and antagonizes distinct effects of TNF-α on tight junction proteins and signaling pathways in intestinal epithelial cells

Intestinal barrier dysfunction is pivotal in the etiology of inflammatory bowel diseases. Combined clinical and endoscopic remission (mucosal healing) in patients who received anti-TNF-alpha therapies suggests restitution of the intestinal barrier, but the mechanisms involved are largely unknown. We therefore investigated the impact of the anti-TNF-alpha antibody adalimumab on barrier function in two in vitro models. Combined stimulation of Caco-2 and T-84 cells with interferon-gamma and TNF-alpha resulted in a significant decrease of transepithelial electrical resistance (TEER) within 6 h that was prevented by adalimumab in concentrations down to 100 ng/ml. Adalimumab furthermore antagonized the appearance of irregular membrane undulations and prevented internalization of tight junction proteins upon cytokine exposure. In addition, TNF-alpha induced a downregulation of claudin-1, claudin-2, claudin-4, and occludin as well as activation of phosphatidylinositol 3-kinase signaling in T-84 but not Caco-2 cells, which was reversed by adalimumab. At the signaling level, adalimumab prevented increased phosphorylation of myosin light chain as well as activation of p38 MAPK and NF-kappa B accompanying the decline in TEER in both model systems. Pharmacological inhibition of NF-kappa B signaling partially prevented the TNF-alpha induced TEER loss, whereas inhibition of p38 worsened barrier dysfunction in Caco-2 but not T-84 cells. Taken together, these data demonstrate that adalimumab prevents barrier dysfunction induced by TNF-alpha both functionally and structurally as well as at the level of signal transduction. Barrier protection might therefore constitute a novel mechanism how anti-TNF-alpha therapy contributes to epithelial restitution and tissue repair in inflammatory bowel diseases.